700 PROGRESS OP ASTRONOMY VOli 1891 ANlJ 1892. 



such superposition occuired two mouths previous to discovery of A 

 by l)i(K>ks, iiud gives for July 8 ;i distaui'c of 190" at 02°. 5 position 

 angle. That the companions were not seen in July, may be naturally 

 ascribed to interference of mooidight up to about July 20, aud after 

 that either to the fact that the attention of observers was not suffi- 

 ciently directed to the phenomenon, or to the fact that the objects had 

 not yet become bright enough to be easily disceruible. We have the 

 evidence of Spitaler that on July 30 and 31 uothing abnormal was 

 noticed with the 27 inch; the slight elongation on those dates, seen by 

 him in A having no relation to the matter in hand. Two nights 

 after, at the time of discovery, Barnard estimated tlie brightness of C 

 at about one-fifth that of ^. It tJien gradually increased in brilliancy, 

 also becoming less diffused and developing a strong condensation and 

 nucleus, until at the end of August it was actually brighter than A al- 

 though only one-third its size. In early Se])tember it was about equal 

 in brightness to A but from tlie middle of that month faded, and be- 

 came larger and more diffuse until it disappeared, late in i^rovember. 

 The faint nucleus of i?, in the beginning ai)pears to liave been a little 

 brighter than thnt of (\ and its coma smaller and less diffused. A])out 

 the middle of August it had grown to be larger and fainter than at 

 first, later more rapidly so, being excessively difficult to see or measure 

 in the first few days of September, and invisible immediately there- 

 after. 1) and E were measured only on the night of discovery, and 

 were seen only at rare intervals until the last time on August 29. 



Such, briefiy described, are the main features as to brightness aiul 

 visibility of these objects. I beg courteously to dissent from the view 

 which has been confidently expressed, that the diffusion and disappear- 

 ance of />, while it was theoretically increasing in brightness, indicate 

 'that it actually dissipated itself into space and absolutely ceased +o 

 exist, if indeed it were not absorbed into the main comet.' Such a con 

 elusion is inherently improbable, unwarranted by any knowledge we 

 possess as to the process of cometary light development, and (;ontra 

 dieted by inferences drawn from other cases, of which only the most 

 analagous need be cited, namely, that of the two nuclei of Biela's comet, 

 the capricious action of which affords a strict counterpart to the present 

 instance. It will be recollected that fitful alternations of visibility 

 occurred in 1840, and especially in 1852, when they repeated theui selves 

 almost from day to day. The two comx)anions were not habitually seen 

 at the same time, but sometimes one, sometimes the other; so that ob- 

 servers could not tell which they were looking at, without comparison 

 with the ephemeris. Thus, in the space of one week, for example, 1852, 

 September 15 to 22, both nuclei were visible, then only the southern, 

 then only the northern, then both together; again only the southern, 

 iind, finally, only the northern, on successive nights, respectively. 



It may be added that there a])pears to be little reason for interpret- 

 ing these remarkable variations of brilliancy as standing in any rela 

 tion of efi'ect with cause wliich jtroduced theiflisruption, either in Bic 



